Search

This paper reports a study of the chemistry of valinomycin, enniatins and related membrane-active depsipeptides that increase alkali metal ion permeability of model and biological membranes. The antimicrobial activity of these compounds and their effect on membranes has been correlated with their cation-complexing ability. The complexing reaction has been studied by spectropolarimetric and conductimetric methods. Nuclear magnetic resonance, optical rotatory dispersion, and infrared spectrophotometric studies have revealed the coexistence of conformers of the cyclodepsipeptides in solution and have led to elucidation of the spatial structure of valinomycin, enniatin B and their K(+) complexes. The effect of the conformational properties of the cyclodepsipeptides on their complexation efficiency and selectivity, surface-active properties and behavior towards phospholipid monolayers, bimolecular phospholipid membranes and a number of biological membrane systems has been ascertained. The studies have clearly shown the feasibility of using cyclodepsipeptides with predetermined structural and conformational parameters as chemical tools for membrane studies. it is suggested that the principle of conformation-dependent cation binding through iondipole interactions may possibly lie at the basis of the mode of action of systems governing the natural ion permeability in biological membranes.

The optical rotatory dispersion curves of all the possible protected diastereoisomeric tri- and tetra-peptides of alanine and serine have been measured in methanol; the protected serine derivatives have also been examined in hexane. Arithmetical treatment of the results enables the contributions of the individual chromophores to the total molecular rotation to be calculated.

The ability of enniatins to bind alkali metal, alkaline earth metal and certain transition metal ions in solution has been investigated. The complexes have been shown to form in 1:1, 2:1 and 3:2 macrocycle:cation ratios; their stability constants have been determined, and the conditions favoring their formation have been established. The enniatins were shown to be complexones of very wide spectrum, displaying low metal ion selectivity in alcoholic solutions. Two basic spatial forms, the non-symmetric N3 form (in nonpolar solvents) and the symmetric P form (in polar solvents) have been disclosed and proposals made as to their conformational parameters. The molecular structure of the enniatin complexes has been established. Independent of the complexed ion species, of the complex stoichiometry, or of the type of solvent, the enniatin backbone of the complex is in the P form. In the 1:1 complexes, the ion is accommodated in the molecular cavity, forming iondipole bonds with all the amide and ester carbonyls. The depsipeptide chain of the enniatins is flexible, permitting “adaptation” of the complexone to the size of the ion, and thus explaining the low selectivity of these complexones. In the 2:1 and 3:2 complexes the cation is sandwiched in between two molecules of the antibiotic at the symmetry axis and interacts mainly with the N-methylamide carbonyls. In these “sandwich” complexes the cation is much better screened from the anion and solvent than in the equimolar complexes and is highly soluble in organic solvents. The data presented here may serve as basis for interpreting the dependence between the structure, metal complexing behavior and membrane-affecting properties in the series of the naturally occurring enniatin ionophores and their synthetic analogs.

THE interaction of a biologically active substance with a selective receptor (for instance, substrate and enzyme) to cause a certain physiological effect is chemically complex, requiring not only a certain minimum of steric congruity of the molecules but also a given electron density distribution in the interacting functional centres. If either of these requirements is not satisfied, the reaction will either not take place at all or its effectiveness will be diminished by several orders of magnitude. It is thus important to discover the limits of steric and electronic matching, both in the rational search for substances with similar, modified or antagonistic action, and to understand the underlying mechanism.

The conformational states of the cyclodecapeptide antamanide and of its Na+ complex have been studied by a number of spectroscopic methods. Two conformers were found for antamanide of which one, existing in non polar solvents has all six NH groups hydrogen bonded. A three dimensional structure of the antamanide·Na+ complex has been proposed containing four intramolecular hydrogen bonds formed by the amide CO and NH groups. The sodium ion is held in the inner cavity by ion-dipole interaction with six amide carbonyls. The proposed structure explains the efficiency and selectivity of the antamanide complexation reaction

The basic principles of the topochemical approach to the investigation of the structure-function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme.

The synthesis of cyclotetradepsipeptides the structure of which has previously been assigned to antibiotics of the enniatin group is described. It was found that these antibiotics cannot be represented by the formulas (I)–(VI).

In this paper we present the results of a systematic numerical analysis of the channeling properties of electrons and positrons in oriented straight and periodically bent diamond(110) crystals. We analyse dependence of the intensity of the radiation emitted on the projectile energy as well as on the bending amplitude. The analysis presented is based on the grounds of accurate numerical simulations of the channeling process. The simulation parameters, such as the crystal orientation, thickness and bending parameters of the crystals as well as the energy of the projectiles, were chosen to match those used in past and ongoing experiments. The peculiarities which appear in the radiation spectra are attributed to the interplay of various radiation mechanisms. The analysis performed can be used to predict and explain future experimental results., Comment: 14 pages, 8 figures, 1 table

A comparison was made of the results of measurements of the continuous attenuation in the 8–12 μ atmospheric "window" under natural conditions with the results of laboratory measurements of the attenuation of CO2 laser radiation by pure water vapor. The results of the laboratory experiments converted to the thickness of the whole atmosphere were in good agreement with the results of measurements under natural conditions. A considerable contribution of the water vapor dimers to atmospheric absorption was confirmed.

The growth of single photoionization corss section in the vicinity of the Kr and Xe d-subshell threshold is given a theoretical explanation.

Йсходя из топохимических предпосылок, предлозен новый принцип модификации биологически активных циклопептидов. Показано, что ретроэнантио-Gly5,10-грам ицидин С обладает активностью, сравнимой с активностью Gly5,10-грамицидина С.

The optical rotatory dispersion curves of all the possible diastereoisomeric tri- and tetra-peptides of alanine and serine have been measured in water, acid, and alkali. Arithmetical treatment of the results enables the contributions of the individual chromophores to the total molecular rotation to be calculated.

Background Protein degradation is a basic cell process that operates in general protein turnover or to produce bioactive peptides. However, very little is known about the qualitative and quantitative composition of a plant cell peptidome, the actual result of this degradation. In this study we comprehensively analyzed a plant cell peptidome and systematically analyzed the peptide generation process. Results We thoroughly analyzed native peptide pools of Physcomitrella patens moss in two developmental stages as well as in protoplasts. Peptidomic analysis was supplemented by transcriptional profiling and quantitative analysis of precursor proteins. In total, over 20,000 unique endogenous peptides, ranging in size from 5 to 78 amino acid residues, were identified. We showed that in both the protonema and protoplast states, plastid proteins served as the main source of peptides and that their major fraction formed outside of chloroplasts. However, in general, the composition of peptide pools was very different between these cell types. In gametophores, stress-related proteins, e.g., late embryogenesis abundant proteins, were among the most productive precursors. The Driselase-mediated protonema conversion to protoplasts led to a peptide generation “burst”, with a several-fold increase in the number of components in the latter. Degradation of plastid proteins in protoplasts was accompanied by suppression of photosynthetic activity. Conclusion We suggest that peptide pools in plant cells are not merely a product of waste protein degradation, but may serve as important functional components for plant metabolism. We assume that the peptide “burst” is a form of biotic stress response that might produce peptides with antimicrobial activity from originally functional proteins. Potential functions of peptides in different developmental stages are discussed. Electronic supplementary material The online version of this article (doi:10.1186/s12870-015-0468-7) contains supplementary material, which is available to authorized users.